1. Field of the Invention
This invention relates to a magnetoresistive transducer, a method for the formation of a magnetic film, and a magnetic recording/reproducing drive, and more particularly to a magneto-resistive transducer for converting a change in the signal magnetic field from a magnetic recording media into a change in the electric resistivity as by the spin valve magnetoresistivity, a method for the formation of a magnetic film, and a magnetic recording drive.
2. Description of the Prior Art
In recent years, the thin film magnetic head which can comply with the trend of magnetic disc devices toward exaltation of recording density and miniaturization has been attracting attention and is demanded to offer improved performance. In the field of the magnetoresistive type reproducing heads (MR head), the MR elements of high performance are now under development. The elements provided with a giant magnetoresistive film capable of yielding a high output without relying on the speed of movement of the magnetic recording media have been of arresting interest. Among other elements of this class, particularly the spin valve magnetoresistive film is renowned because it can be relatively easily formed. Moreover, this film has been attracting special attention because the MR elements provided with the film have a large change in electric resistance in a low magnetic field as compared with the other MR elements.
The magnetoresistive transducers that utilize the spin valve magnetoresistance have been disclosed in U.S. Pat. No. 5,206,590 and JP-A-06-60,336, for example.
FIG. 1A is a perspective view illustrating a spin valve magnetoresistive transducer of the conventional principle and FIG. 1B is a cross section taken through FIG. 1A along the line I--I.
As illustrated in FIG. 1A and FIG. 1B, a ground layer 2 formed of tantalum (Ta), a free magnetic layer 3 consisting of an NiFe film 3b and a Co.sub.90 Fe.sub.10 film 3a, a nonmagnetic metal layer 4 formed of a Cu film, a Co.sub.90 Fe.sub.10 (pinning magnetic layer) 5, an antiferromagnetic layer 6, and a cap layer 7 are sequentially superposed on an altic substrate 1.
The component layers from the ground layer 2 through the cap layer 7 are patterned in an oblong shape. On the cap layer 7 constituting the uppermost layer, outlet electrodes 8a and 8b are formed in the opposite terminal parts across a sense area (SA). The change in magnetoresistance in the sense area (SA) is measured as the change in voltage.
The pinning magnetic layer 5, by exchange coupling with the antiferromagnetic layer 6, generates an exchange coupling magnetic field in the direction of the X axis in a X,Y,Z coordinate system. The magnetization of the pinning magnetic layer 5 is consequently fixed in the direction of the X axis and this magnetization is not changed due to a signal magnetic field. The free magnetic layer 3 is magnetized in the direction of the Y axis in the absence of a signal magnetic field and this magnetization is easily changed by a signal magnetic field. The magnetoresistance is changed in proportion to the cosine of the angle, .theta., to be formed by the direction of the magnetization of the free magnetic layer 3 and the direction of the magnetization of the pinning magnetic layer 5 (cos .theta.).
The free magnetic layer 3 is a two-layer film consisting of an NiFe film 3b and a Co.sub.90 Fe.sub.10 film 3a. It, therefore, yields more than twice as high magnetoresistive output as when the free magnetic layer 3 is formed solely of the NiFe film 3a.
When a magnetic head is formed with the MR element described above, however, a resist film as an interlayer insulating film must be hardened by a heat treatment to be performed at a temperature in the range of 230 to 300.degree.. In this case, the rate of change of the electric resistivity, .DELTA..rho., is lowered by this heat treatment as illustrated in FIG. 8. It is inferred that this decline of the rate of change of the electric resistivity, .DELTA..rho., is induced particularly by the inclusion of Cu into the NiFe film 3a of the free magnetic layer 3.
This phenomenon has the problem of incurring a decrease in the reproduced output of the magnetic head.